1. Field
The present invention relates to transceivers and more particularly to a Ku-band satellite transceiver with a mixed dielectric printed circuit board (PCB) interface containing a coaxial to microstrip transition which is connected to a surface mount diplexer.
2. Background
Starting in the late 1980's companies such as Qualcomm Inc. developed satellite communication systems which provided two-way communication between trucks and a centralized hub for the trucking industry. In the case of Qualcomm Inc., an integral part of its satellite based system is a mobile satellite data modem (SDM) unit which is mounted on the outside of the truck cabin to establish an airlink to a geostationary Ku-band transponder. These SDM units contain sophisticated Ku-band transceivers which are exposed to a wide variety of environmental conditions such as extreme weather, shock, and vibration. Among other components the Ku-band transceiver's radio frequency (RF) front end with its interface to the antenna is crucial for the performance of transmit and receive chains. The configuration of this interface needs to provide a low loss, continuous transmission line link between the antenna feed and the microwave circuits on the transceiver's printed circuit board which can withstand mentioned environmental extremes.
Presently, most interfaces consist of a connectorized link between the antenna feed and a single layer microwave board implementation of a diplexer which isolates the receive chain from the transmit chain.
The present invention combines the Ku-band transceiver's microwave section together with its ancillary analog/digital circuitry on a mixed dielectric hybrid PCB stack-up which has the high frequency substrate laminated on top of a standard multi layer FR-4 style core. In order to keep the microwave section compact and to provide an easy implementation for the coaxial antenna feed to printed circuit board transition, the diplexer is implemented as a surface mountable part using a ceramic substrate and is described in a co-pending patent application. In order to provide a low loss transition of less than (<) 1 dB at Ku-band frequencies from the microwave section of the satellite transceiver's PCB to its antenna, the interface needs to provide a good impedance match between the surface mount diplexer and the antenna feed (antenna probe). The microwave performance of this transition is further challenged since the PCB is a hybrid construction that consists of mixed dielectrics—at microwave frequencies highly lossy multi layer FR-4 style laminate and a single layer high frequency style laminate. On the mechanical side, this interface has to operate reliably in a rugged environment, such as a trucking environment, that is characterized through continuous vibration, shock, and a wide temperature range (from −40 degrees Celsius to +85 degree Celsius). From a manufacturing point of view the interface has to meet design for manufacturability standards in a high volume production environment.
A poorly designed/performing PCB interface would manifest itself in two scenarios:
Degraded (decreased) transmit power in the transmit chain of the satellite transceiver. This translates into increased transition insertion loss lowering the transmit power.
Degraded (increased) noise figure in the receive chain of the satellite transceiver. This translates into increased transition insertion loss increasing the noise figure.